The present invention pertains generally to data recording/recovery devices, and more particularly to a method for rewriting data that fails a check-after-write test to ensure data integrity.
Data storage devices, which are used in both short- and long-term capacities, are an integral part of modern computer systems. While factors such as costs, device form factor, storage media size and capacity, and recording and recovery times are of high importance, of primary concern is the ability to maintain data integrity.
Accordingly, many tape drives include a check-after-write scheme whereby data is verified by a read head as the data is recorded onto the tape. For example, in a helical scan tape drive, in which data is written in tracks in an alternate-azimuth helical pattern by a pair alternate azimuth adjacent write heads mounted on a rotating drum, the newly recorded data is verified half a drum rotation later by a pair of alternate azimuth read heads located 180 degrees relative to the pair of write heads.
Whenever a check-after-write failure occurs, the write operation is suspended and the tape is repositioned backwards to allow enough space to accelerate again to the forward operating speed, and the track containing the xe2x80x9cfailedxe2x80x9d data is overwritten by a new track on which the xe2x80x9cfailedxe2x80x9d data is attempted to be rewritten. The failed data had to be rewritten before data which followed it in address sequence could be recorded onto the tape due to the format requirement calling for recording in-sequence.
The prior art backhitching sequence for rewriting xe2x80x9cbadxe2x80x9d data is problematic. First, the time required for a backhitching cycle increases data recording time and delays the host system by causing an interruption if data from the host had achieve a maximum throughput xe2x80x9cstreamingxe2x80x9d mode. In addition, because backhitching induces extremely high transient forces that greatly increase tape wear and reduce the mechanical reliability of the drive, the backhitch operation can seriously impact data reliability.
The backhitching sequence can be avoided by simply rewriting tracks that contain xe2x80x9cbadxe2x80x9d data further down the tape without stopping the process. However, this methodology has the disadvantage that if the rewrite count is high, a significant portion of the tape is occupied by duplicate tracks containing mainly redundant xe2x80x9cgoodxe2x80x9d data, thereby reducing the storage capacity of the tape.
Accordingly, a need exists for a method for rewriting xe2x80x9cbadxe2x80x9d data without engaging in a backhitching sequence and without the overhead requirements of rewriting full mainly-redundant or mainly-empty tracks.
The present invention is a novel method and apparatus for performing rewrites at the packet level by allowing data to be recorded onto tracks on a magnetic media in any address sequence. Local packet address information is included in the track packet itself to allow track packets to be written to the storage medium in any addressing order. This allows a single packet to be rewritten along a later track among other track packets that are being recorded for the first time, thereby reducing rewrite track overhead and eliminating the requirement for a lengthy backhitching sequence.